The present invention relates to an efficient transport of encoded traffic in optical communications networks employing synchronous signaling techniques, such as networks employing Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) signaling formats.
A large number of wavelength-division multiplexed (WDM) point-to-point transmission systems and WDM networks presently exist. Many of these systems have been designed to support a fixed number of wavelengths and a predetermined data format. SONET is a common framing format for data transport in long-haul and metropolitan-area WDM carrier networks. The SONET frame provides a convenient standard mechanism to multiplex and transport circuit-switched traffic in high-speed backbones and support network functions. As a result of its beneficial characteristics, SONET framing is presently used in most WDM systems.
In contrast to SONET framing, many packet-switched local area networks (LANs) use framing defined in the long-established Ethernet standard. Unlike SONET, Ethernet and other LAN protocols rely on non-synchronous signaling techniques. Ethernet has become the dominant LAN technology such that virtually all data traffic originates and terminates as an Ethernet frame with an IP header. Ethernet has evolved to become a switched technology in which there are no protocol related distance limitations and the only distance limitation remaining is due to the physical layer. Furthermore, Ethernet supports a wide range of transmission rates ranging from 10 Megabits per second (Mbps) for Ethernet service, 100 Mbps for Fast Ethernet (FE) service, 1 Gigabit per second (Gbps) for Gigabit Ethernet (GbE) service, and up to 10 Gbps Dense WDM (DWDM) and possibly higher rates in the near future.
Ethernet typically connects at the LAN edge via a router to a variety of WAN technologies, such as SONET/SDH, ATM, and T1. Carriers and service providers have addressed the demands for Ethernet, FE, GbE, and DWDM with high performance L2/L3 switches, optical fiber infrastructure, long reach Ethernet interfaces, and optical switches. However, problems result in meeting these demands due to the scarcity and expense of WAN bandwidth, the need for additional customer premises equipment, and the installation and administration of unfamiliar WAN interfaces. It is desirable to combine WAN technologies, such as SONET/SDH, with Ethernet by more efficiently utilizing the SONET/SDH bandwidth to transparently offer end to end carrier class Ethernet service with diverse bit rates.
Because SONET and GbE have been separately optimized for transport and data networking, these signaling mechanisms have been treated in an isolated manner. For instance, a typical WDM network with OC-48 interfaces can accept only SONET-framed traffic at the OC-48 rate (2.488 Gbps). A mechanism is not presently available for efficiently and transparently accepting variable-sized packets transmitted at a non-SONET rate, such as the 1.25 Gbps rate of a GbE network. Even though a SONET framer may be used to translate a GbE signal into an OC-48 SONET signal, this approach would result in an inefficient utilization of the available bandwidth (only about 40% of the available bandwidth is used) at each wavelength transporting such traffic.